1. Field of the Invention
The present invention relates to a method of manufacturing a multilayer wiring board including the step of impregnating a raw material composition of a thermosetting resin in a porous laminated product including two or more porous layers and a wiring layer provided between the porous layers and formed in any of the porous layers and step of curing or half curing them, and a multilayer wiring board obtained thereby. They are particularly useful as a technique for easily manufacturing a multilayer wiring board having the large number of laminations.
2. Description of the Related Art
In recent years, an increase in a density has been required for a wiring board with a reduction in the size and weight of electronic devices or the like and a wiring layer has had a multilayer structure correspondingly. For the structure of a multilayer wiring board, generally, an insulating layer and a wiring layer having a patter formed thereon are sequentially laminated and the adjacent wiring layers are conductively connected to each other through an inner via hole. As the conductive connecting method, there have been known a method of plating the inner peripheral surface of a via hole, a method of plating the internal space of the via hole to form a metal column, a method of filling a conductive paste in the internal space of the via hole and the like.
As a method of manufacturing the multilayer wiring board having such an interlayer connecting structure, a method of using a lamination unit integrating a prepreg to be an insulating layer and a wiring layer (or a metal foil having no pattern formed thereon) for repeating lamination and heating and pressurization, or a method of sequentially forming the insulating layer and the wiring layer alternately have been put into practical use. In general, the interlayer connecting structure is formed at the middle step between repeating processes.
In the manufacturing method described above, however, the heating and pressurization is repeated for each layer. Consequently, the number of steps is increased corresponding to the number of laminations. Therefore, such a manufacturing method has a poor efficiency for manufacturing a wiring board having a multilayer structure. Referring to the multilayer wiring board thus obtained, moreover, there is a problem in that the insulating layers have a low bonding strength and precision in alignment of the lamination is poor due to the sequential execution of the laminating steps.
Therefore, it is an object of the present invention to provide a method of manufacturing a multilayer wiring board in which the step of integrating laminated products is carried out at the same time so that a multilayer wiring board having a large number of laminations can easily be manufactured, and the multilayer wiring board thus obtained hardly causes a problem of the bonding strength between insulating layers or precision in alignment of the laminations, and the multilayer wiring board obtained thereby.
On the other hand, an increase in the mounting density of an electronic component has recently been required. Consequently, there have been proposed some structures in which a passive component such as a resistor or a capacitor or an active component such as a semiconductor chip is incorporated in the multilayer wiring board. For example, there have been a method of arranging a chip component, a method of forming an element by utilizing a part of a wiring layer, a method of combining both of them and the like.
In these methods, however, there is a problem in that a cavity is to be always provided in a portion in which a chip component is provided or a space between the formed elements is to be maintained in any way.
Therefore, it is another object of the present invention to provide a method of manufacturing a multilayer wiring board in which a space between chip components or various elements can easily be maintained and the multilayer wiring board obtained thereby.